Astronomers say they’ve discovered the most distant body ever observed in our solar system, a potential dwarf planet that’s about 11 billion miles from the sun.
Its nickname? “Farout.”
The far-out object — which is also known by its more official but less colorful designation, 2018 VG18 — was detected with Japan’s 8-meter Subaru Telescope in Hawaii during a campaign to look for extremely distant solar system objects, including a hypothetical Planet X or Planet Nine.
Further observations to confirm Farout’s distance and determine its brightness and color were made with the 6.5-meter Magellan Telescopes at the Carnegie Institution for Science’s Las Campanas Observatory in Chile. The observations were reported today in a circular distributed by the International Astronomical Union’s Minor Planet Center.
The discovery team includes Carnegie’s Scott Sheppard, the University of Hawaii’s David Tholen and Northern Arizona University’s Chad Trujillo. NAU’s Will Oldroyd assisted with the follow-up observations.
Farout’s orbit isn’t yet known well enough to determine exactly how far out it will eventually get, or whether it could have been perturbed by the gravitational influence of an as-yet-unseen object that’s several times more distant from the sun. Planet X’s existence has been inferred because of a pattern of eccentricities seen in the orbits of other objects on the solar system’s edge.
“2018 VG18 is much more distant and slower moving than any other observed solar system object, so it will take a few years to fully determine its orbit,” Sheppard said in a news release. “But it was found in a similar location on the sky to the other known extreme solar system objects, suggesting it might have the same type of orbit that most of them do.”
The object’s current distance from the sun is about 120 astronomical units, with each of those units representing the 93-million-mile distance between Earth and the sun. In comparison, Pluto is about 34 AU from the sun. The dwarf planet Eris is currently the second-farthest-out solar system object at a distance of 96 AU. Yet another object known as Sedna is currently 90 AU from the sun, but traveling in a highly eccentric orbit that takes it more than 10 times farther out as it makes its 11,400-year rounds.
Millions of solar system objects are much farther out than Farout, in a cometary halo known as the Oort Cloud. However, those objects are too far out to be individually identified.
Sheppard and his colleagues suspect that Farout is a 300-mile-wide dwarf planet similar in makeup to the Saturnian moon Enceladus, based on a pinkish color that’s typically associated with ice-rich objects.
“All that we currently know about 2018 VG18 is its extreme distance from the sun, its approximate diameter, and its color,” Tholen said. “Because 2018 VG18 is so distant, it orbits very slowly, likely taking more than 1,000 years to take one trip around the sun.”
Douglas Vakoch, president of METI International, told GeekWire in an email that the discovery of Farout proves the value of the hunt for Planet X.
“We still don’t know whether Planet X really exists, but in the search for it, astronomers have found the most distant body yet discovered in our solar system,” Vakoch wrote. “Farout is the first object discovered beyond 100 AU — a hundred times the distance between the Earth and Sun.”